URINARY SYSTEM regulate the concentration of the major ions,
such as Na+, Cl−, K+, HCO3
4. REGULATION OF A RED BLOOD CELL
SYNTHESIS- The kidneys secrete a hormone,
erythropoietin, that stimulates the synthesis
of red blood cells in red bone marrow
KIDNEYS
Are bean-shaped organs.
Lie behind peritoneum
(retroperitoneal)
The liver is superior to the right
kidney, causing the right kidney to be
slightly lower than the left
Internal and External Structure of the
kidneys:
Renal Capsule- is the innermost, tough and
fibrous material covering each kidney
Adipose capsule- made up of adipose tissue
which gives the kidney a protective cushion
against impacts
Renal fascia- outer layer; composed of
connective tissues that surrounds the kidney
and attached firmly to the posterior
abdominal wall
Hilum- located at the middle side of the
kidney where the renal artery and nerves
The urinary system is the major excretory system enter and where the renal vein and ureter
of the body. exit the kidneys
URINARY SYSTEM includes organs such as:
a. Kidneys Kidneys are organized into 2 major regions:
b. Ureters
c. Urinary bladder Renal Cortex- outer region; light in color
d. Urethra
Renal medulla- inner region; darker-reddish
The urinary system consists of two kidneys, brown area
the primary excretory organs.
Each kidney’s excretory products are carried Renal pyramids-The medulla has many
by a ureter to a single urinary bladder. basically triangular regions with a striped
The urinary bladder is emptied of the waste appearance, the renal, or medullary pyramids
liquid by the urethra.
FUNCTIONS OF URINARY SYSTEM: Renal column- The pyramids are separated
by extensions of cortex-like tissue, the renal
1. EXCRETION- The kidneys filter waste columns.
products from the blood.
Large molecules, such as proteins, remain in Renal pelvis- Medial to the hilum is a flat,
the blood, basin like cavity, the renal pelvis, which is
whereas smaller molecules and ions enter the continuous with the ureter leaving the hilum
filtered fluid. As the fluid flows through the
kidneys, it is slowly modified until it is Calyces- Extensions of the pelvis, calyces,
converted into urine. form cup-shaped areas that enclose the tips
2. REGULATION OF BLOOD VOLUME AND of the pyramid and collect urine, which
PRESSURE-The kidneys can produce either a continuously drains from the tips of the
large volume of dilute urine or a small volume pyramids into the renal pelvis.
of concentrated urine, depending on the
hydration level of the body. Through urine Renal artery- supplies oxygenated blood to
production, the kidneys regulate blood the kidneys which divides into segmental
volume and hence blood pressure arteries as it approaches the hilum, and
3. REGULATION OF BLOOD SOLUTE each segmental artery gives off several
CONCENTRATIONS- The kidneys help branches called interlobar arteries
Arcuate arteries- At the cortex-medulla 2. Glomerular capsule (Bowman
junction, interlobar arteries give off arcuate capsule)- is an indented, double-
arteries, which curve over the medullary walled chamber surrounding the
pyramids. glomerulus. From the glomerular
capsule, the filtered fluid flows into
the proximal convoluted tubule region
of the renal tubule.
Together, the structures in the corpuscle
make up the filtration membrane.
Filtration membrane- performs the first
major step in urine production. Urine
production begins when the filtration
membrane filters the blood
RENAL TUBULE
Once the blood is filtered, the resulting
fluid is modified to form urine as it passes
through each section of the renal tubule.
The first section is the proximal
NEPHRON- is the histological and functional convoluted tubule. It is approximately 14
unit of the kidney mm long
There are approximately 1.3 million As the proximal convoluted tubule
nephrons distributed throughout the continues descending
cortex and medulla of each kidney. toward the medulla, the cell type begins
It consists of specialized structures to change. At this point, the renal tubule
including small tubes that are called is called the nephron loop. Every
renal tubules. nephron loop has two limbs: (1) the
Nephron has 4 separate regions: descending limb and (2) the ascending
1. Renal corpuscle-filters the blood limb.
2. Proximal convoluted tubule- return The thick part of the ascending limb
filtered substances to the blood returns toward the renal corpuscle and
3. Nephron loop-helps conserve water ends by transitioning to the distal
and solutes convoluted tubule
4. Distal convoluted tubule-rids the blood The distal convoluted
of additional wastes tubule is shorter than the
proximal convoluted tubule
Several distal convoluted
tubules connect to a single
collecting duct
RENAL CORPUSCLE
The filtration portion of the nephron
Consists of:
1. Glomerulus- is a network of
capillaries twisted around each other
like a ball of yarn
Fluid filtered from the
glomerular capillaries is called
the filtrate
URINE PRODUCTION
The primary function of the kidney is
regulation of body fluid composition.
The kidney is the organ that sorts the
substances from the blood for either
removal in the urine or return to the
blood.
Substances that are waste products,
toxins, and excess materials are
permanently removed from the body,
whereas other substances need to be
preserved to maintain homeostasis.
The structural components that
perform this sorting are the nephrons,
the functional units of the kidney
FILTRATION
is a nonspecific process whereby materials
are separated based on size or charge.
Filtration is the first step in urine
production.
All blood components except blood
cells and most proteins can leave the
glomerular capillaries and enter the
glomerular capsule as filtrate. Glomerular filtration rate (GFR)- rate of
It is the filtrate that will be modified filtrate formed per minute.
into urine. The glomerular filtration rate (GFR) is very
stable. It does not
significantly change even if systemic blood
pressure drops as low
as 90 mm Hg or rises as high as 180 mm Hg.
TUBULAR REABSORPTION
is the transport of water and solutes from the
filtrate into the
blood.
Proper tubular reabsorption is critical
in preventing the body from becoming
overly dehydrated and deficient in
important materials.
The filtrate leaves the lumen of the
glomerular capsule and flows first
through the proximal convoluted
tubule, into the nephron loop and the
distal convoluted tubule, and then
finally into the collecting ducts.
Solutes reabsorbed from the lumen of
the renal tubule to the interstitial fluid
includes amino acids, glucose, and
fructose, as well as Na+, K+, Ca2+,
HCO3−, and Cl−
The small volume of the filtrate that The micturition reflex is activated when the
forms urine contains urea, uric acid, urinary bladder wall is stretched as urine fills
creatinine, K+, and other substances. the urinary bladder. Integration of the
micturition reflex occurs in the sacral region
of the spinal cord and is modified by centers
in the pons and cerebrum
TUBULAR SECRETION
is the movement of nonfiltered substances
from the blood into the filtrate.
These substances include toxic
byproducts of metabolism and drugs
or molecules not normally produced
by the body.
URETERS
are tubes through which urine flows from the
kidneys to the urinary bladder.
URINARY BLADDER
is a hollow, muscular container that lies in the
pelvic cavity just
posterior to the symphysis pubis.
The urinary bladder acts as a reservoir
for urine until it can be eliminated
relatively quickly at an appropriate
time and place.
The urinary bladder can stretch to
hold a large urine volume.
At its maximum volume, the urinary
bladder can contain 1 L (about 1
quart) of urine, but discomfort
becomes noticeable when urine
volume exceeds approximately 500
mL
Detrusor muscle- smooth muscle in
the urinary bladder that forces urine
out of urinary bladder.
URETHRA
transports urine to the outside of the body
Internal urethral sphincter- prevents
urine leakage from the urinary bladder
External urethral sphincter- allows a
person to voluntarily start or stop the
flow of urine through the urethra.
Urination is also called micturition.
